If you could travel back in time, what could you change? The world, its past and its present all belong to the Creator. All is as He wills it to be.
Perhaps you could replay some crucial scenes and distance yourself from the mess that occurred. Perhaps you could jump in and grab credit for some of the good.
But for that, you don't need a time machine. All you need is to stand right where you are and say, "I messed up. I lost my chance. I learned my lesson and now I will do things differently."
You will change yourself. You will change your past. You will say, "I am no longer the person who lived in that past."
In fact, you do have a time machine.
Based on letters and talks of the Rebbe, Rabbi M. M. Schneerson 
